KR101766702B1 - Method and apparatus of estimating signal to noise ratio in wireless communication system - Google Patents

Abstract

A method and apparatus for estimating a signal-to-noise ratio (SNR) in a wireless communication system are provided. The SNR estimation apparatus includes a sector preamble selector for selecting a preamble signal for each sector for a plurality of sectors in a received signal that has undergone Fast Fourier Transform (FFT) output, a sector preamble selector for selecting a sector preamble signal and a preamble reference signal A signal power estimator for estimating a power of a received signal for each sector based on the correlation signal, a noise power estimator for estimating a noise power of each sector based on the correlation signal, An adder for subtracting the selected minimum value from the powers of the received signals for each sector and outputting pure power for each sector, and a selector for selecting the pure power for each sector as the selected And a divider for dividing the SNR by the minimum value.

Description

Field of the Invention [0001] The present invention relates to a method and apparatus for estimating a signal-to-noise ratio in a wireless communication system,

The present invention relates to wireless communication, and more particularly, to a method and apparatus for estimating a signal-to-noise ratio (SNR) in a wireless communication system in a wireless communication system.

In the case of a broadband wireless communication system, effective transmission and reception techniques and utilization methods have been proposed to maximize the efficiency of limited radio resources. One of the systems considered in the next generation wireless communication system is an Orthogonal Frequency Division Multiplexing (OFDM) system capable of attenuating the inter-symbol interference (ISI) effect with low complexity. OFDM converts serial data symbols into N parallel data symbols, and transmits the data symbols on N separate subcarriers. The subcarriers maintain orthogonality at the frequency dimension. Each of the orthogonal channels experiences mutually independent frequency selective fading, thereby reducing the complexity at the receiving end and increasing the interval of transmitted symbols, thereby minimizing intersymbol interference.

Orthogonal frequency division multiple access (OFDMA) refers to a multiple access method in which a part of subcarriers available in a system using OFDM as a modulation scheme is independently provided to each user to realize multiple access. OFDMA provides a frequency resource called a subcarrier to each user, and each frequency resource is provided independently to a plurality of users and is not overlapped with each other. Consequently, frequency resources are allocated mutually exclusively for each user.

The UE can estimate a signal-to-noise ratio (SNR) of a received signal. The estimated SNR can be applied in various ways. Advanced Modulation and Coding (AMC) can be applied using the SNR, and the UE can report the SNR to the BS through a message or feedback channel in a MIMO (Multiple-Input Multiple-Output) system to stabilize the link performance. In addition, the system capacity can be improved by using a high-order modulation scheme.

On the other hand, it is important to accurately calculate the noise power in order to accurately estimate the SNR of the received signal. In general, when the distance between the terminal and the base station is close to zero, the strength of the received signal is high and the error of estimation of noise power becomes large as the intensity of the received signal increases. Therefore, the accuracy of the SNR estimation of a received signal with a high SNR is relatively inferior.

Therefore, a more accurate SNR estimation method is required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for estimating a signal-to-noise ratio (SNR) in a wireless communication system in a wireless communication system. In particular, the present invention provides a method and apparatus for estimating the SNR of a received signal using a frame signal in a 3-sector OFDM (Orthogonal Frequency Division Multiplexing) system.

In an aspect, a signal-to-noise ratio (SNR) estimation apparatus is provided in a wireless communication system. The SNR estimator includes a sector preamble selector for selecting a sector preamble signal for a plurality of sectors in a received signal that has undergone Fast Fourier Transform (FFT) output, a sector preamble selector connected to the sector preamble selector, A correlator for outputting a correlation signal by performing correlation between a preamble signal and a preamble reference signal for each sector, a signal power estimator connected to the correlator, for estimating a power of a received signal for each sector based on the correlation signal, A noise power estimator for estimating a noise power for each sector based on the correlation signal, a minimum value selector connected to the noise power estimator for selecting a minimum value among the noise powers for each sector, And the minimum value selector, and subtracts the selected minimum value from the power of the received signal for each sector An adder for outputting pure power for each sector, and a divider connected to the minimum value selector and the adder, for dividing the net power of each sector by the selected minimum value and calculating an SNR.

The number of the plurality of sectors may be three.

The preamble signal for each sector can be allocated to each sector in three subcarriers.

The sub-carriers to which the preamble signals of the respective sectors are allocated may not overlap with each other in the sectors.

In another aspect, an Orthogonal Frequency Division Multiplexing (OFDM) receiver is provided in a wireless communication system. The OFDM receiver includes an antenna for receiving a signal, an RF (Radio Frequency) processor connected to the antenna for processing a received signal, a guard interval removing unit connected to the RF processor, an FFT unit connected to the guard interval removing unit, An equalizer connected to the FFT unit, and the SNR estimating unit connected to the FFT unit.

In another aspect, a method for estimating SNR in a wireless communication system is provided. The SNR estimation method includes: selecting a preamble signal for each sector for a plurality of sectors in a received signal that has undergone FFT output; correlating a preamble signal and a preamble reference signal for each sector to output a correlation signal; Estimating a power of a received signal for each sector based on a correlation signal, estimating a noise power for each sector based on the correlation signal, selecting a minimum value of the noise power for each sector, Subtracting the selected minimum value from the power of the received signal to output the net power for each sector, and calculating the SNR by dividing the net power for each sector by the selected minimum value.

The SNR estimation performance can be improved when the actual SNR (Signal-to-Noise Ratio) is high.

1 is an example of a preamble structure of the IEEE 802.16e system.
2 is a block diagram illustrating a typical OFDM receiver in an OFDMA system.
3 is a block diagram illustrating an SNR estimator of an OFDM receiver.
4 is a block diagram illustrating an SNR estimator of an OFDM receiver by the proposed SNR estimation method.
5 to 7 are graphs illustrating performance of the proposed SNR estimation method.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification. And a detailed description thereof will be omitted to omit descriptions of portions that can be readily understood by those skilled in the art.

Throughout the specification and claims, when a section is referred to as " including " an element, it is understood that it does not exclude other elements, but may include other elements, unless specifically stated otherwise.

The following description will be made on the assumption that the present invention is applicable to a CDMA system such as Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), and Single Carrier Frequency Division Multiple Access And can be used in various wireless communication systems. CDMA may be implemented in radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. The TDMA may be implemented in a wireless technology such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in wireless technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and Evolved UTRA (E-UTRA). IEEE 802.16m is an evolution of IEEE 802.16e, providing backward compatibility with systems based on IEEE 802.16e. UTRA is part of the Universal Mobile Telecommunications System (UMTS). The 3rd Generation Partnership Project (3GPP) LTE (Long Term Evolution) is a part of E-UMTS (Evolved UMTS) using Evolved-UMTS Terrestrial Radio Access (E-UTRA). It adopts OFDMA in downlink and SC -FDMA is adopted. LTE-A (Advanced) is the evolution of 3GPP LTE.

For clarity of description, IEEE 802.16e is mainly described, but the technical idea of the present invention is not limited thereto.

1 is an example of a preamble structure of the IEEE 802.16e system.

The first symbol of the downlink transmission may be used for transmission of the preamble signal. Three different preamble carrier-sets may be defined with different sub-carrier assignments according to each Fast Fourier Transform (FFT) size. Subcarriers can be modulated by a BPSK (Binary Phase Shift Keying) modulation scheme that is boosted by a particular pseudo-noise (PN) code.

Referring to FIG. 1, a frequency domain in one cell is divided into three sectors. Sector 0 (s = 0) represents the subcarrier indices 0, 3, 6, ... The preamble carrier set 0 including the preamble carrier set # 0. Sector 1 (s = 1) is the subcarrier index 1, 4, 7, ... And transmits the preamble signal to the preamble carrier set 1. [ Sector 2 (s = 2) consists of subcarrier indices 2, 5, 8, ... To the preamble carrier set 2. The preamble carrier set 2 transmits the preamble signal. Since the frequency domain is divided into three sectors and different subcarriers are allocated, the noise power can be obtained for each sector.

2 is a block diagram illustrating a typical OFDM receiver in an OFDMA system.

The OFDM receiver includes an antenna 101, a radio frequency (RF) processing unit 102, a guard interval removing unit 103, an FFT unit 104, an equalizer 105, and a signal-to-noise ratio (SNR) ). The received signal received through the antenna 101 passes through the RF processing unit 102 and the guard interval removing unit 103. The SNR estimator 106 estimates the SNR by selecting a preamble signal among the reception signals that have been output through the FFT 104. That is, when an OFDM transmitter transmits a signal of a known pattern as a preamble signal, the OFDM receiver that receives the signal estimates the SNR using the preamble signal. At this time, the preamble structure of IEEE 802.16e of FIG. 1 can be used. According to the preamble structure of FIG. 1, the preamble signal allocates a code string for every three subcarriers per sector in the frequency domain.

3 is a block diagram illustrating an SNR estimator of an OFDM receiver.

3, the SNR estimator 106 includes a preamble selector 201, a correlator 202, a signal power estimator 203, a noise power estimator 204, an adder 205, and a divider 206 ). The correlator 202 performs a cross-correlation with the preamble signal selected by the preamble selector 201 and the reference signal of the preamble signal generated by the receiver through the FFT output. The correlator 202 outputs the correlation signal. The signal power estimator 203 estimates the signal power based on the correlation signal, and the noise power estimator 204 estimates the noise power based on the correlation signal. The divider 206 divides the estimated signal power by the estimated noise power to calculate an SNR. The signal power used at this time is the power of the entire received signal minus the noise power, which can be performed by the adder 205.

It is important to obtain the noise power accurately to obtain the accurate SNR of the received signal. The present invention proposes a method of accurately estimating the SNR by considering the minimum noise power per sector as the noise power of a corresponding sector in a system in which different subcarriers are allocated per sector to reduce inter-cell interference. do.

4 is a block diagram illustrating an SNR estimator of an OFDM receiver by the proposed SNR estimation method.

4, the SNR estimator 106 includes a sector-specific preamble selector 201, a correlator 202, a signal power estimator 203, a sector-0 noise power estimator 301, a sector- A sector 2 noise power estimation unit 303, a minimum value selection unit 304, an adder 205, and a divider 206. [ The sector-specific preamble selector 201 selects a preamble signal for each sector of the received signal that has undergone the FFT output. The correlator 202 performs cross-correlation between the preamble signal selected for each sector and the reference signal of the preamble signal generated by the receiver, and outputs a correlation signal. The signal power estimator 203 estimates the signal power based on the correlation signal. The sector 1 noise power estimation unit 301, the sector 1 noise power estimation unit 302 and the sector 2 noise power estimation unit 303 estimate the noise power of sector 0, sector 1 and sector 2, respectively, do. The minimum value selector 304 selects the minimum value among the noise powers of the respective sectors estimated by the sector-0 noise power estimator 301, the sector-1 noise power estimator 302 and the sector-2 noise power estimator 303 . The divider 206 divides the estimated signal power by the minimum value of the noise power per sector to calculate the SNR. The signal power used at this time is obtained by subtracting the minimum value of the noise power per sector from the power of the entire received signal, and this can be performed by the adder 205.

Hereinafter, the operation of the SNR estimating unit will be described by an equation.

Assuming correct synchronization at the receiver, the FFT output Y _m ⁽ⁿ⁾ of the _mth subcarrier in the n th OFDM symbol can be expressed by Equation (1).

&Quot; (1) "

A; (Additive White Gaussian Noise AWGN), where X _m ⁽ⁿ⁾ is the transmission signal of the m th subcarrier of the n-th OFDM symbol, N _m ⁽ⁿ⁾ is additive white Gaussian noise with zero mean and a standard deviation σ ² of. H _m ⁽ⁿ⁾ is the channel response of the m-th subcarrier of the n-th OFDM symbol. N _used is the number of subcarriers that can be _used in the frequency domain. Since the preamble signal is assigned a code sequence for every three subcarriers, the subcarrier index m of Equation (1) can be defined as Equation (2).

&Quot; (2) "

이다. 따라서 각 섹터의 FFT 출력은 수학식 3으로 표현할 수 있다.In Equation (2), k denotes a preamble symbol index, and s denotes a sector index.

to be. Therefore, the FFT output of each sector can be expressed by Equation (3).

&Quot; (3) "

On the other hand, the noise power of each sector is obtained based on F _{k, s} defined by Equation (4) under the assumption that the channel characteristics of adjacent subcarriers are the same (H _k ≒ H _k-1 ≒ H _{k +} .

&Quot; (4) "

If the frequency domain is divided into three sectors, the terminal receives all the signals transmitted from each sector. If the received signal is divided into signals per sector, Equation (5) is obtained.

Equation (5)

In Equation (5), H _{k, 0} , H _{k, 1} , H _{k, 2} represent independent channel characteristics of each sector, and X _{k, 0} , X _{k, 1} X _{k, 2} represent the OFDM symbol index n = Represents a signal transmitted from each sector. (5) and a code string for each sector, and the noise power for each sector can be calculated by Equation (6).

&Quot; (6) "

On the other hand, _{Fk, s} is influenced by the received power of the signal. This can be expressed by Equation (7).

&Quot; (7) "

는 f(P_s)가 증가함에 따라 함께 증가한다. 따라서 수학식 8에 의해서 선택된 각 섹터별 잡음 전력의 최소값이 잡음 전력으로 사용될 수 있다.According to equations (6) and (7)

It will increase along with increasing f (P _s). Therefore, the minimum value of the noise power for each sector selected by Equation (8) can be used as the noise power.

&Quot; (8) "

The SNR of each sector can be calculated using the minimum value of the noise power for each selected sector. The SNR of each sector in one OFDM symbol in which the OFDM symbol index n is ignored can be calculated by Equation (9).

&Quot; (9) "

는 해당 섹터의 신호 전력을 나타낸다. 이때 해당 섹터의 신호 전력은 수신 신호의 전체 전력에서 상기 선택된 각 섹터별 잡음 전력의 최소값을 뺀 값이다.In Equation (9)

Represents the signal power of the corresponding sector. At this time, the signal power of the corresponding sector is a value obtained by subtracting the minimum value of the noise power of each selected sector from the total power of the received signal.

Hereinafter, the performance of the proposed SNR estimation method will be described. The simulation conditions are shown in Table 1.

Parameters Value Channel BW 10MHz Frame length 5ms FFT size (N _FFT ) 1024 Preamble N _used 852 OFDMA symbol time 102.9s Subcarrier spacing 10.94 kHz Sampling frequency 11.2 MHz Preamble power boosting 9dB

5 to 7 are graphs illustrating performance of the proposed SNR estimation method.

In FIGS. 5 to 7, the power ratio of each sector is represented by (P ₀ , P ₁ , P ₂ ). P _i is the signal received from each sector, which is a function of the distance to the terminal. Referring to FIG. 5, when the SNR is estimated in a vehicle moving at 60 km / h, the SNR estimated by the proposed SNR estimation method is more accurate than the SNR estimated by the conventional technique even when the actual SNR is increased have. In particular, assuming that the sector is sector 0, the actual SNR can be accurately estimated when (P ₀ , P ₁ , P ₂ ) = ( ₁ , ₀ , 0). This is because it is possible to obtain accurate noise power because only noise is carried in the subcarriers of other sectors. 6 shows SNR estimation performance in case of a pedestrian moving at 3 km / h, and FIG. 7 shows SNR estimation performance in case of a vehicle moving at 60 km / h.

The present invention may be implemented in hardware, software, or a combination thereof. (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In software implementation, it may be implemented as a module that performs the above-described functions. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders . It will also be understood by those skilled in the art that the steps shown in the flowchart are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention.

The above-described embodiments include examples of various aspects. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

Claims (13)

In a wireless communication system,
A sector-specific preamble selector for selecting a preamble signal for each sector for a plurality of sectors in a received signal that has undergone Fast Fourier Transform (FFT) output;
A correlator connected to the sector-specific preamble selector for performing correlation between a preamble signal and a preamble reference signal for each sector and outputting a correlation signal;
A signal power estimator connected to the correlator for estimating a power of a received signal for each sector based on the correlation signal;
A noise power estimator connected to the correlator for estimating a noise power of each sector based on the correlation signal;
A minimum value selector connected to the noise power estimator for selecting a minimum value among noise powers of the respective sectors;
An adder connected to the signal power estimating unit and the minimum value selecting unit to subtract the selected minimum value from the power of the received signal for each sector and output pure power for each sector; And
And a divider coupled to the minimum value selector and the adder, for dividing the net power of each sector by the selected minimum value to calculate a signal-to-noise ratio (SNR). The method according to claim 1,
Wherein the number of the plurality of sectors is three. The method according to claim 1,
Wherein the preamble signal for each sector is allocated to each sector by three subcarriers. The method of claim 3,
Wherein the subcarriers to which the preamble signals for the respective sectors are allocated do not overlap with each other in the sectors. The method according to claim 1,
Wherein the noise power for each sector is calculated by the following equation.

only,

K is a preamble symbol index, and s is a sector index. F _{k, s} is defined by the following equation.

X _{k, s} is a signal transmitted from each sector, and Y _{k, s} is a received signal received by each sector. The method according to claim 1,
Wherein the SNR is calculated by the following equation.

only,

Is the net power of each sector,

Is the minimum value of the noise power for each sector,

k is a preamble symbol index, s is a sector index, n is an OFDM symbol index, and Y _{k and s} are reception signals received in the respective sectors. In a wireless communication system,
An antenna for receiving a signal;
An RF (Radio Frequency) processor connected to the antenna for processing a received signal;
A guard interval removing unit connected to the RF processor;
A Fast Fourier Transform (FFT) unit connected to the guard interval removing unit;
An equalizer connected to the FFT unit; And
An Orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division Multiplexing) receiver including the SNR estimating apparatus of claim 1 connected to the FFT unit. In a wireless communication system,
Selecting a preamble signal for each sector for a plurality of sectors in a received signal that has undergone an FFT (Fast Fourier Transform) output;
Outputting a correlation signal by performing correlation between a preamble signal and a preamble reference signal for each sector;
Estimating a power of a received signal for each sector based on the correlation signal;
Estimating a noise power of each sector based on the correlation signal;
Selecting a minimum value among the noise power for each sector;
Subtracting the selected minimum value from the power of the received signal for each sector and outputting pure power for each sector; And
Dividing the net power of each sector by the selected minimum value to calculate a signal-to-noise ratio (SNR). 9. The method of claim 8,
And the number of the plurality of sectors is three. 9. The method of claim 8,
Wherein the preamble signal for each sector is allocated to each sector by three subcarriers. 11. The method of claim 10,
Wherein the subcarriers to which the preamble signals for the respective sectors are allocated do not overlap with each other in the sectors. 9. The method of claim 8,
Wherein the noise power of each sector is calculated by the following equation.

only,

K is a preamble symbol index, and s is a sector index. F _{k, s} is defined by the following equation.

X _{k, s} is a signal transmitted from each sector, and Y _{k, s} is a received signal received by each sector. 9. The method of claim 8,
Wherein the SNR is calculated by the following equation.

only,

Is the net power of each sector,

Is the minimum value of the noise power for each sector,

k is a preamble symbol index, s is a sector index, n is an OFDM symbol index, and Y _{k and s} are reception signals received in the respective sectors.

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